1. Field
The present invention relates generally to telecommunications, and more specifically, to multi-carrier communications.
2. Background
In wireless communication systems, dual-carrier or multi-carrier terminals are increasingly being used for simultaneously carrying voice traffic and non-voice data traffic. In this regard, a multi-carrier terminal is a terminal having the capability of transmitting information on more than one carrier simultaneously. Many such terminals might be employed in a code division multiple access (CDMA) wireless communication system. For example, in an application requiring high-speed data and voice traffic to be transmitted simultaneously, it would be possible to use a multi-carrier terminal with one carrier supporting the CDMA2000—1x standard for voice traffic and another carrier supporting the CDMA2000—1xEv-DO standard, which is optimized for transmission of data traffic. The transmitting terminal would use one carrier, designated the “DO” carrier, for transmission of data traffic, and would use another carrier, designated as the “1x” carrier for transmission of voice traffic. A description of these systems may be found in their corresponding “3rd Generation Partnership Project 2” (3GPP2) standards. The CDMA2000—1x system is specified in “cdma2000 Introduction Release C,” 3GPP2 C.S0001-C v1.0, May 2002. The CDMA2000—1xEv-DO system is specified in “cdma2000 High Rate Packet Data Air Interface Specification,” 3GPP2 C.S0024-0 v4.0, October 2002.
Effective transmitter design for a multi-carrier terminal could embrace multiple power amplification circuits, each dedicated to one carrier and each including a power amplifier. However, limitations on space, manufacturing cost, power consumption and other factors dictate the need to share resources among the carriers, including power amplification circuitry. Accordingly, it would be advantageous to utilize a single power amplifier for transmission of a plurality of carriers transmitted by a multi-carrier terminal.
A power amplifier is an RF element of a transmitter that amplifies a modulated carrier signal for transmission by an antenna. Although a power amplifier may be depicted and referred to as if it were a single element, those skilled in the art will appreciate that such a device may comprise one or more stages.
If a multi-carrier terminal has a single power amplifier for simultaneous transmission of different types of carrier signals, the power amplifier may be subject to power constraints imposed by spectral emission requirements, by on-board battery capacity, and also by any priority among the carriers. For example, in a combined CDMA2000—1x_/_CDMA2000—1xEV-DO wireless communication system, presume that the 1x carrier takes precedence in the allocation of transmitter power over the DO carrier in order to avoid degradation in the voice cell coverage. Because the 1x carrier has priority over the DO carrier, the only power limitations imposed on the 1x carrier other than the peak power of the power amplifier are battery capacity and spectrum emission control schemes to limit the transmit power of mobile stations. Therefore, if the DO carrier has lower priority than the 1x carrier, it would be desirable to allocate to the DO carrier only some portion of transmitter power not used by the 1x carrier.
Furthermore, when the 1x and DO carriers are simultaneously transmitted, it would be desirable that the power of the multi-carrier waveform transmitted by the multi-carrier terminal be limited to a level such that spectral emission goals are not compromised. It is further desirable to preserve these power constraints while requiring little modification to the equipment and operations of existing communication systems.
Therefore, there is a need in the art for a scheme for allocating the transmit power of a carrier according to a priority in a multi-carrier terminal in which a single power amplifier is utilized for transmitting a plurality of carrier signals simultaneously.